The invention relates generally to an exhaust gas sensor system and, more specifically, to a system and method for protecting an exhaust gas sensor from particulate emissions.
Vehicle and industrial exhaust emissions typically include carbon monoxide, oxides of nitrogen, hydrocarbons and particulates, carbon dioxide, or the like. These substances are a significant contributor to local air pollution, which may result in poor visibility, including smog, and haze and erosion of building surfaces.
Because of concerns about pollution, many vehicles and industrial systems include devices to help reduce the emission of undesirable substances. Such devices typically include an exhaust sensor that detects a level of undesirable substances in the exhaust stream. Exhaust sensors may be adapted to measure levels of oxygen, hydrocarbons and nitrous oxides in the exhaust stream. Sensors may also be used to sense, for example, when an exhaust gas content switches from rich to lean, or lean to rich. The output of the exhaust sensor may be used by a combustion control unit to improve the quality of the exhaust stream by controlling various combustion unit parameters.
Constituents of exhaust gas such as particulates, and water droplets may foul the exhaust gas sensing device, resulting in degraded performance of the emission control device. For example, a fouled sensor may have reduced ability to accurately detect the constituent components of an exhaust gas stream. Shielding the sensor from direct contact with large particulate matter in the exhaust stream may reduce the occurrence of sensor fouling.
While preventing fouling of the exhaust sensor is important, a countervailing design consideration is to ensure sufficient airflow in the vicinity of the exhaust gas sensor. Sufficient flow is required to allow the sensor to provide an accurate reading in a given response time to facilitate effective control of the combustion unit.
An improved system and method for balancing the competing design goals of providing sufficient flow past an exhaust gas sensor while protecting the sensor from being fouled by large particles in the exhaust stream is desirable.